1. Field of the Invention
The present invention relates to an apparatus for controlling a salient-pole DC brushless motor by controlling armature currents of the motor based on a rotor angle thereof which is detected without using a position detection sensor.
2. Description of the Related Art
For energizing a DC brushless motor to produce a desired torque, it is necessary to apply voltages to the armatures in suitable phases corresponding to the electric angle of the rotor (hereinafter referred to as xe2x80x9crotor anglexe2x80x9d) which has magnetic poles. There have been proposed various processes of detecting a rotor angle without using a position detection sensor in order to reduce the cost of the DC brushless motor and a motor control apparatus therefor by way of dispensing with any position detection sensor for detecting the rotor angle.
The inventors of the present application have proposed a rotor angle detector for detecting a rotor angle of a DC brushless motor without using a position detection sensor in an earlier patent application (Japanese patent laid-open publication No. 2002-320398). The disclosed rotor angle detector operates as follows: When high-frequency voltages are added to drive voltages that are applied to three-phase armatures of a salient-pole DC brushless motor, the rotor angle detector uses a detected value of a current flowing through the first-phase armature, a detected value of a current flowing through the second-phase armature, and high-frequency components depending on the high-frequency voltages to calculate a sine reference value depending on the sine value of a twofold angle which is twice the rotor angle of the DC brushless motor and a cosine reference value depending on the cosine value of the twofold angle. Then, the rotor angle detector calculates the rotor angle of the DC brushless motor using the sine reference value and the cosine reference value which have been calculated. When a rotor angle is detected using the sine reference value and the cosine reference value, the detected rotor angle has a period of 180 degrees. In order to detect a rotor angle in a range of 360 degrees, it is necessary to detect the orientation of the magnetic poles of the rotor at the time the motor starts rotating.
If the time required to detect the orientation of the magnetic poles of the rotor is long, then the motor suffers a delayed start.
It is therefore an object of the present invention to provide an apparatus for controlling a DC brushless motor to reduce the time required to detect the orientation of the magnetic poles of the rotor of the DC brushless motor.
According to the present invention, there is provided an apparatus for controlling a salient-pole DC brushless motor having armatures in three phases, comprising voltage applying means for applying drive voltages to the armatures, high-frequency adding means for adding high-frequency voltages to the drive voltages, first current detecting means for detecting a current flowing through an armature in a first phase of the armatures in the three phases, second current detecting means for detecting a current flowing through an armature in a second phase of the armatures in the three phases, and reference value extracting means for extracting a sine reference value depending on the sine value of a twofold angle which is twice a rotor angle of the motor and a cosine reference value depending on the cosine value of the twofold angle, using a first current value detected by the first current detecting means and a second current value detected by the second current detecting means when the high-frequency voltages are added to the drive voltages by the high-frequency adding means, and high-frequency components depending on the high-frequency voltages.
The apparatus also has rotor angle calculating means for calculating a rotor angle of the motor using the sine reference value and the cosine reference value, three-phase/dq converting means for handling the motor as an equivalent circuit having a q-axis armature disposed on an q-axis in the direction of magnetic fluxes from a rotor of the motor and a d-axis armature disposed on a d-axis which is perpendicular to the q-axis, and calculating a detected q-axis current flowing through the q-axis armature and a detected d-axis current flowing through the d-axis armature based on the rotor angle of the motor which is calculated by the rotor angle calculating means, the first current value, and the second current value, current control means for determining the drive voltages in order to eliminate a q-axis current difference which is the difference between the detected q-axis current and a predetermined q-axis command current and a d-axis current difference which is the difference between the detected d-axis current and a predetermined d-axis command current, and magnetic pole detecting means for carrying out a magnetic pole detecting process to detect the orientation of the magnetic poles of the rotor based on a magnetic pole reference value calculated by a predetermined calculating process, depending on the sine reference value and the cosine reference value which are extracted by the reference value extracting means when the q-axis command value is set to a predetermined magnetic pole detecting current.
The current control means performs a proportional plus integral process on the difference between the detected q-axis current and the q-axis command current to calculate the q-axis current difference and also performs a proportional plus integral process on the difference between the detected d-axis current and the d-axis command current to calculate the d-axis current difference when the magnetic pole detecting process is not carried out, and performs an integral process only on the difference between the detected q-axis current and the q-axis command current to calculate the q-axis current difference and also performs an integral process only on the difference between the detected d-axis current and the d-axis command current to calculate the d-axis current difference when the magnetic pole detecting process is carried out.
With the above arrangement, when the magnetic pole detecting process is carried out, the current control means performs an integral process only on the difference between the detected q-axis current and the q-axis command current to calculate the q-axis current difference and also performs an integral process only on the difference between the detected d-axis current and the d-axis command current to calculate the d-axis current difference. Therefore, when the q-axis command current is set to the magnetic pole detecting current, the current control means controls the current flowing through the q-axis armature to pass the magnetic pole detecting current through the q-axis armature without causing a delay which would otherwise result from an integral process.
In this case, the time spent after the q-axis command current is set to the magnetic pole detecting current until currents depending on the magnetic pole detecting current are detected by the first current detecting means and the second current detecting means. Therefore, the time required until the sine reference value and the cosine reference value depending on the magnetic pole detecting current and the magnetic pole reference value calculated depending on the magnetic pole detecting current are obtained.
Accordingly, the time required to detect the orientation of the magnetic poles of the rotor of the motor based on the magnetic pole reference value according to the magnetic pole detecting process is shortened.
Also, according to the present invention, there is provided a method for controlling a salient-pole DC brushless motor having armatures in three phases, an apparatus for controlling the DC brushless motor comprising voltage applying means for applying drive voltages to the armatures, high-frequency adding means for adding high-frequency voltages to the drive voltages, first current detecting means for detecting a current flowing through an armature in a first phase of the armatures in the three phases, second current detecting means for detecting a current flowing through an armature in a second phase of the armatures in the three phases, and reference value extracting means for extracting a sine reference value depending on the sine value of a twofold angle which is twice a rotor angle of the motor and a cosine reference value depending on the cosine value of the twofold angle, using a first current value detected by the first current detecting means and a second current value detected by the second current detecting means when the high-frequency voltages are added to the drive voltages by the high-frequency adding means, and high-frequency components depending on the high-frequency voltages, rotor angle calculating means for calculating a rotor angle of the motor using the sine reference value and the cosine reference value, and three-phase/dg converting means for handling the motor as an equivalent circuit having a q-axis armature disposed on a q-axis in the direction of magnetic fluxes from a rotor of the motor and a d-axis armature disposed on a d-axis which is perpendicular to the q-axis, and calculating a detected q-axis current flowing through the q-axis armature and a detected d-axis current flowing through the d-axis armature based on the rotor angle of the motor which is calculated by the rotor angle calculating means, the first current value, and the second current value.
Moreover, the method for controlling the DC brushless motor comprises the step of determining the drive voltages in order to eliminate a q-axis current difference which is the difference between the detected q-axis current and a predetermined q-axis command current and a d-axis current difference which is the difference between the detected d-axis current and a predetermined d-axis command current, performing a magnetic pole determination process for detecting the orientation of the magnetic poles of the rotor based on a magnetic pole reference value calculated by a predetermined calculating process, depending on the sine reference value and the cosine reference value which are extracted by the reference value extracting means when the q-axis command value is set to a predetermined magnetic pole detecting current, and performing a proportional plus integral process on the difference between the detected q-axis current and the q-axis command current to calculate the q-axis current difference and also performing a proportional plus integral process on the difference between the detected d-axis current and the d-axis command current to calculate the d-axis current difference when the magnetic pole detecting process is not performed, and performing an integral process only on the difference between the detected q-axis current and the q-axis command current to calculate the q-axis current difference and also performing an integral process only on the difference between the detected d-axis current and the d-axis command current to calculate the d-axis current difference when the magnetic pole detecting process is performed.
With the above arrangement, the time spent after the q-axis command current is set to the magnetic pole detecting current until currents depending on the magnetic pole detecting current are detected by the first current detecting means and the second current detecting means. Therefore, the time required until the sine reference value and the cosine reference value depending on the magnetic pole detecting current and the magnetic pole reference value calculated depending on the magnetic pole detecting current are obtained.
Accordingly, the time required to detect the orientation of the magnetic poles of the rotor of the motor based on the magnetic pole reference value according to the magnetic pole detecting process is shortened and thus the current flowing in the armature can be controlled.
The apparatus and method for controlling a salient-pole DC brushless motor according to the present invention sets a first magnetic pole detecting current and a second magnetic pole detecting current which is opposite in direction to the first magnetic pole detecting current as the magnetic pole detecting current, and detects the orientation of the magnetic poles of the rotor based on the difference between a first magnetic pole reference value calculated by the predetermined calculating process depending on the sine reference value and the cosine reference value which are extracted by the reference value extracting means when the first magnetic pole detecting current is set, and a second magnetic pole reference value calculated by the predetermined calculating process depending on the sine reference value and the cosine reference value which are extracted by the reference value extracting means when the second magnetic pole detecting current is set. between a first magnetic pole reference value calculated by the predetermined calculating process depending on the sine reference value and the cosine reference value which are extracted by the reference value extracting means when the first magnetic pole detecting current is set, and a second magnetic pole reference value calculated by the predetermined calculating process depending on the sine reference value and the cosine reference value which are extracted by the reference value extracting means when the second magnetic pole detecting current is set.
With the above arrangement, as described in detail later on, the sign of the difference between the first magnetic pole reference value calculated when the first magnetic pole detecting current is set as the magnetic pole detecting current and the second magnetic pole reference value calculated when the second magnetic pole detecting current is set as the magnetic pole detecting current is inverted depending on the orientation of the magnetic poles of the rotor. Therefore, the orientation of the magnetic poles of the rotor can be detected based on the difference between the first magnetic pole reference value and the second magnetic pole reference value.
The reference value extracting means extracts the sine reference value and the cosine reference value respectively according to the following equations (1), (2):                               V          ⁢                      xe2x80x83                    ⁢          s                =                              ∫            0                                          2                ⁢                                  xe2x80x83                                ⁢                π                            ω                                ⁢                                    {                                                cos                  ⁢                                      xe2x80x83                                    ⁢                  2                  ⁢                                      xe2x80x83                                    ⁢                  ω                  ⁢                                      xe2x80x83                                    ⁢                  t                  ⁢                                      xe2x80x83                                    ⁢                                                            cos                      ⁡                                              (                                                                              ω                            ⁢                                                          xe2x80x83                                                        ⁢                            t                                                    +                                                                                    2                              3                                                        ⁢                            π                                                                          )                                                              ·                    I                                    ⁢                                      xe2x80x83                                    ⁢                  u                                -                                  cos                  ⁢                                      xe2x80x83                                    ⁢                  2                  ⁢                                      xe2x80x83                                    ⁢                  ω                  ⁢                                      xe2x80x83                                    ⁢                  t                  ⁢                                      xe2x80x83                                    ⁢                  cos                  ⁢                                      xe2x80x83                                    ⁢                  ω                  ⁢                                      xe2x80x83                                    ⁢                                      t                    ·                    I                                    ⁢                                      xe2x80x83                                    ⁢                  w                                            }                        ⁢                          ⅆ              t                                                          (        1        )                                          V          ⁢                      xe2x80x83                    ⁢          c                =                  -                                    ∫              0                                                2                  ⁢                                      xe2x80x83                                    ⁢                  π                                ω                                      ⁢                                          {                                                      sin                    ⁢                                          xe2x80x83                                        ⁢                    2                    ⁢                                          xe2x80x83                                        ⁢                    ω                    ⁢                                          xe2x80x83                                        ⁢                    t                    ⁢                                          xe2x80x83                                        ⁢                                                                  cos                        ⁡                                                  (                                                                                    ω                              ⁢                                                              xe2x80x83                                                            ⁢                              t                                                        +                                                                                          2                                3                                                            ⁢                              π                                                                                )                                                                    ·                      I                                        ⁢                                          xe2x80x83                                        ⁢                    u                                    -                                      sin                    ⁢                                          xe2x80x83                                        ⁢                    2                    ⁢                                          xe2x80x83                                        ⁢                    ω                    ⁢                                          xe2x80x83                                        ⁢                    t                    ⁢                                          xe2x80x83                                        ⁢                    cos                    ⁢                                          xe2x80x83                                        ⁢                    ω                    ⁢                                          xe2x80x83                                        ⁢                                          t                      ·                      I                                        ⁢                                          xe2x80x83                                        ⁢                    w                                                  }                            ⁢                              ⅆ                t                                                                        (        2        )            
where Vs: the sine reference value, Vc: the cosine reference value, Iu: the first current value, Iw: the second current value, and a: the angular velocity of the high-frequency voltages.
With the above arrangement, the reference value extracting means can calculate the sine reference value (Vs) and the cosine reference value (Vc) from the first current value (Iu), the second current value (Iw), and the angular velocity of the high-frequency voltages. The rotor angle calculating means can calculate the rotor angle of the motor using the sine reference value (Vs) and the cosine reference value (Vc). The magnetic pole detecting means can detect the orientation of the magnetic poles of the rotor based on the magnetic pole reference value which is calculated depending on the sine reference value (Vs) and the cosine reference value (Vc).
The above and other objects, features, and advantages of the present invention will become apparent from the following description when taken in conjunction with the accompanying drawings which illustrate a preferred embodiment of the present invention by way of example.